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High-Power Synchronous HBLED
Drivers with Rapid Current Pulsing
? V IN × I LED × ( t R + t F ) × f SW ?
? ?
Inductor Selection
The switching frequency, peak inductor current, and
allowable ripple at the output determine the value and
size of the inductor. Selecting higher switching frequen-
cies reduces inductance requirements, but at the cost
of efficiency. The charge/discharge cycle of the gate
and drain capacitance in the switching MOSFETs cre-
ate switching losses worsening at higher input volt-
ages, since switching losses are proportional to the
square of the input voltage. The MAX16821A/
MAX16821B/MAX16821C operate up to 1.5MHz.
Choose inductors from the standard high-current, sur-
face-mount inductor series available from various manu-
facturers. Particular applications may require
custom-made inductors. Use high-frequency core mate-
rial for custom inductors. High Δ I L causes large peak-to-
peak flux excursion increasing the core losses at higher
frequencies. The high-frequency operation coupled with
high Δ I L reduces the required minimum inductance and
makes the use of planar inductors possible.
The following discussion is for buck or continuous
boost-mode topologies. Discontinuous boost, buck-
boost, and SEPIC topologies are quite different in
regards to component selection. Use the following
equations to determine the minimum inductance value:
Buck regulators:
Switching MOSFETs
When choosing a MOSFET for voltage regulators, con-
sider the total gate charge, R DS(ON) , power dissipation,
and package thermal impedance. The product of the
MOSFET gate charge and on-resistance is a figure of
merit, with a lower number signifying better perfor-
mance. Choose MOSFETs optimized for high-frequen-
cy switching applications. The average current from the
MAX16821A/MAX16821B/MAX16821C gate-drive out-
put is proportional to the total capacitance it drives
from DH and DL. The power dissipated in the
MAX16821A/MAX16821B/MAX16821C is proportional
to the input voltage and the average drive current. The
gate charge and drain capacitance losses (CV 2 ), the
cross-conduction loss in the upper MOSFET due to
finite rise/fall time, and the I 2 R loss due to RMS current
in the MOSFET R DS(ON) account for the total losses in
the MOSFET. Estimate the power loss (PD MOS_ ) in the
high-side and low-side MOSFETs using the following
equations:
PD MOS _ HI = ( Q G × V DD × f SW ) +
? ? +
2
R DS ( ON ) × I 2 RMS ? HI
L MIN =
( V INMAX ? V LED ) × V LED
V INMAX × f SW × Δ I L
where Q G , R DS(ON ), t R , and t F are the upper-switching
MOSFET’s total gate charge, on-resistance, rise time,
and fall time, respectively.
? I 2 VALLEY + I 2 PK + I
?
I RMS ? HI =
VALLEY × I PK ? ×
Boost regulators:
L MIN =
( V LED ? V INMAX ) × V INMAX
V LED × f SW × Δ I L
D
? 3
For the buck regulator, D is the duty cycle, I VALLEY =
(I OUT - Δ I L / 2) and I PK = (I OUT + Δ I L / 2).
( I
) ×
2 2 ( 1 ? D )
I RMS ? LO = VALLEY + I PK + I VALLEY × I PK
V CL ? Δ I CL ?
I LPEAK = + ? ?
where V LED is the total voltage across the LED string.
The average current-mode control feature of the
MAX16821A/MAX16821B/MAX16821C limits the maxi-
mum peak inductor current and prevents the inductor
from saturating. Choose an inductor with a saturating
current greater than the worst-case peak inductor cur-
rent. Use the following equation to determine the worst-
case current in the average current-mode control loop.
R S ? 2 ?
where R S is the sense resistor and V CL = 0.030V. For
the buck converter, the sense current is the inductor
current and for the boost converter, the sense current is
the input current.
PD MOS _ LO = ( Q G × V DD × f SW ) + R DS ( ON ) × I 2 RMS ? LO
3
Input Capacitors
The discontinuous input-current waveform of the buck
converter causes large ripple currents in the input
capacitor. The switching frequency, peak inductor cur-
rent, and the allowable peak-to-peak voltage ripple
reflected back to the source dictate the capacitance
requirement. The input ripple is comprised of Δ V Q
(caused by the capacitor discharge) and Δ V ESR
(caused by the ESR of the capacitor).
18
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相关代理商/技术参数
MAX16821EVKIT+
制造商:Maxim Integrated Products 功能描述:HIGH-POWER SYNCHRONOUS HBLED DRIVER - Boxed Product (Development Kits)
MAX16822AASA/V+
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822AASA/V+T
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822AASA+
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822AASA+T
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822BASA+
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822BASA+T
功能描述:LED照明驱动器 2MHz HB w/MOSFET & HSide Crnt Sense RoHS:否 制造商:STMicroelectronics 输入电压:11.5 V to 23 V 工作频率: 最大电源电流:1.7 mA 输出电流: 最大工作温度: 安装风格:SMD/SMT 封装 / 箱体:SO-16N
MAX16822BEVKIT+
功能描述:LED 照明开发工具 MAX16822B Eval Kit RoHS:否 制造商:Fairchild Semiconductor 产品:Evaluation Kits 用于:FL7732 核心: 电源电压:120V 系列: 封装: